Conventionally, turbine engines firstly comprise, starting from upstream, one or more compressor modules arranged in series, which compress the air sucked into an air inlet. The air is then introduced into a combustion chamber, where it is mixed with a fuel and burned. The combustion gases pass through one or more turbine modules which drive the compressor(s). The gases are lastly ejected either into an exhaust nozzle to produce a propulsive force or onto a free turbine to produce the power which is recovered from a propeller shaft.
The current bypass turbojet engines having a high bypass ratio, or turbofans, comprise a plurality of compressor stages, in particular a low-pressure compressor (LP) and a high-pressure compressor (HP) which belong to the primary body of the engine. Upstream of the low-pressure compressor, a large movable-blade wheel, or fan, is arranged, which supplies both the primary flow passing through the LP and HP compressors and the cold flow, or secondary flow, which is directed directly towards a cold-flow exhaust nozzle, referred to as the secondary exhaust nozzle. The fan is driven by the rotating shaft of the LP body and generally rotates at the same speed as the shaft. However, it may be advantageous to rotate the fan at a rotational speed which is less than that of the LP shaft, in particular when the fan is very large, in order to better adapt the fan aerodynamically. For this purpose, a reducer is arranged between the LP shaft and a fan shaft, which supports the fan. Such a design is described in particular in FR 1251655 and FR 1251656, which were filed on 23 Feb. 2012.
Modern turbine engines are conventionally produced in the form of an assembly of modules which can comprise fixed portions and movable portions. A module is defined as a sub-assembly of a turbine engine which has geometric features in the region of the interfaces thereof with the adjacent modules which are precise enough for the module to be able to be delivered individually, and which has been subjected to specific balancing when it comprises rotating portions. The assembly of the modules makes it possible to form a complete engine, by reducing as much as possible the balancing and pairing operations of the parts which interface with one another. The fan, the fan shaft and the reducer generally form part of the same module, which is referred to as a fan module.
The rotating parts, such as the rotating shaft(s), the compressor(s) and the turbine(s), are supported by structural parts, which are referred to as the intermediate casing at the front and the exhaust casing at the rear, by means of bearings which are enclosed in vessels for the lubrication and the cooling thereof. Turbine engines thus generally comprise at least two lubrication vessels, one located at the front, which contains the bearings positioned at the side of the compressors or the fan, and one located at the rear, which contains the bearings positioned at the side of the turbines. These vessels are formed by an assembly of movable walls and fixed walls, between which are positioned devices, of the labyrinth seal type, to ensure the required sealing therebetween.
In current turbine engines having reducers, the reducer is generally driven directly by the LP shaft, by means of splines formed on the front end portion of the shaft, which cooperate with a toothed wheel of the reducer which is positioned in the region of the inner cylindrical wall thereof.
This solution has a major disadvantage in that it is incompatible with the modularity which is desired for modern engines. Indeed, it is necessary to be able to disassemble the engine into a small number of large elements, which are referred to as major modules and are formed by assembling a plurality of basic modules. In this case, it is desirable to be able to decompose an engine, whether it be for pre-assembly or disassembly, into three major modules, a first major module being formed, upstream, by the low-pressure compressor modules, a second major module being formed by the high-pressure portions and a third major module being formed, downstream, by the low-pressure turbine modules.
In order to carry out this disassembly, it is necessary to disconnect the first major module of the LP shaft which either remains attached to the LP turbine module or is removed from the engine. The removal of the LP shaft thus breaks the continuity of the casing of the front sealed vessel and compromises the sealing thereof. The disassembly of the shaft is thus accompanied by a draining of the oil of the vessel, the amount of which is relatively large due to the lubrication to be carried out of the pinions of the reducer. Precautions must be taken by the maintenance staff in order to prevent the soiling created by this oil, which spreads in an uncontrollable manner and which it is advantageous to recover in order, among other things, to carry out subsequent reassembly.
Furthermore, when the vessel is open, external soiling, during maintenance, can contaminate the oil of the vessel. This problem has even more of an effect on the proper operation of a reducer having plain bearings, by comparison with rolling bearings, the reducer requiring a “good quality” oil.